Field of the Invention
The present invention relates to an antenna device. In particular, the present invention relates to a planar structure having a high surface impedance, and an antenna device employing this planar structure.
Description of the Related Art
In recent years, research has been conducted on technology related to an electromagnetic band gap structure (hereinafter “EBG structure”) that blocks the propagation of electromagnetic waves in a specific frequency bandwidth. One conceivable EBG structure has a structure in which rectangular patch conductors are arranged in a matrix in the same plane with a constant gap interval, and conductive vias from the patch conductors are connected to ground conductors arranged parallel to the patch conductors. In this structure, the set of one patch conductor, one ground conductor, and one conductive via is called a mushroom structure due to its shape. Besides blocking electromagnetic waves, this EBG structure also exhibits an effect of a artificial magnetic conductor that has a high surface impedance in a specific frequency bandwidth. By focusing on this artificial magnetic conductor characteristic and using the EBG structure for antenna dimension lowering, there is expectation for realizing an effective artificial magnetic conductor type low-dimensioned antenna.
With conventional artificial magnetic conductor type low-dimensioned antennas that employ an EBG structure, it has only been possible to realize a structure in which one EBG structure is provided for one antenna element, and therefore it has been difficult to achieve dimension lowering in a multiband antenna.